Fully enclosed tunable reciprocating air column sifter

ABSTRACT

A reciprocating air column sifter includes rigid, fully enclosed speaker and screen housings which define air chambers of sufficient volume to allow reciprocal air movement. A flexible diaphragm is stretched across the opening between the chambers and can be tightened and loosened to tune the sifter. The diaphragm is carried by the speaker housing and is stretched across an upstanding rim on the screen housing, and is adjusted by tightening and loosening screws holding the two housings together. There are three such screws, and they are connected by a chain for simultaneous movement.

United States Patent [56] References Cited UNITED STATES PATENTS [72] Inventor Robert L. Schurrer Milwaukee, Wis.

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[52] US. [51] Int. [50] FieldofSearch.........................

PATENTEDDEB Han 35251 355 SHEET 1 0F 3 INVENTOR ROBERT L. SCHURRER ATTORNEY PATENTEHDEC mm 3.625355 sum 2 [IF 3 INVENTOR ROBERT L. SCHURRER ATTORNEY PATENT EU DEC 7|97| SHEET 3 OF 3 1- 7. 3 /ll 45 g k 47 '9 f5: 48 4/ ,7 A K 4 INVENTOR ROBERT L.SCHURRER ATTORNEY BACKGROUND OF THE INVENTION Reciprocating air column sifters have numerous applications and configurations, ranging from relatively small precision laboratory sifters to large industrial sifters designed for efficiency and high output. Although there are problems peculiar to each application, the principle of operation of the reciprocating air column sifter is the same in all cases. The screen, or screens, are placed in an air column and the material to be sifted is deposited on top of the screen. A reciprocal movement of the air in the column is generated by means of a dynamic speaker or othe'r'vibrator mounted at the top of the air column, and this reciprocal air movement greatly enhances the sifting action. A reciprocating air column sifter of the industrial type is shown in US. Pat. No. 3,410,400, issued to C. W. Ward et al.

Especially if the reciprocating air column sifter is to be used for industrial purposes, it must be capable of sifting large quantities of material efiiciently, and to have the highest efficiency it is desirable to match the mechanical resonant frequency of the sifter to the power source frequency. This can be done by varying power frequency, but this requires expensive oscillators nand it is preferable to work instead with the mechanical resonant frequency. It is particularly desirable to be able to tune the mechanical system to a frequency of approximately 60 cycles per second so that the sifter can be operated at maximum efiiciency off a standard power supply.

A small laboratory sifter can be structurally designed to be and remain in tune with a standard power source. An industrial sifter, however, requires variable tuning means because of the variations encountered in the quantities and the types of materials being sifted. In the Ward patent cited above, there is an adjustable elastic tuning diaphragm in the wall of the speaker housing and another elastic diaphragm in the wall of the speaker housing and another elastic diaphragm in the wall of the speaker housing and another elastic diaphragm in the wall of the screen housing. This provides for effective tuning, but because the diaphragms are exposed to both the interior and exterior of the air column enclosure, they present certain problems. Although they are covered with protective screens, they are subject to physical damage which can result in detuning and escape of material. More importantly, the diaphragms vibrate in response to the reciprocating air inside the enclosure and transmit this sound to the outside like the cone of a loudspeaker. In large industrial sifters this sound can be quite intense and uncomfortable for those working near the machine.

SUMMARY OF THE INVENTION The applicant has discovered that an adequate amount of adjustment in the resonant frequency of the air column enclosure can be accomplished by adjusting the tension of a diaphragm enclosed entirely within the air column; and the sifter of this invention includes a rigid, fully enclosed housing with an adjustable diaphragm across the air column within the housing. Since there is no exposed diaphragm, workers in the surrounding area are not exposed to unnecessary noise, and the sifter is less subject to damage. It is the general objective of the invention to provide a fully enclosed tunable sifter which is efficient, versatile and durable while being economical and simple to manufacture and use. A further specific objective is to provide a tuning means which is accessible while the sifter is running and is easy to operate. Another further specific objective of the invention is to provide a sifter in which the adjustable diaphragm seals off the vibrator housing and, therefore, serves a second function as a protective cover for the vibrator when the sifter is disassembled.

Other objects and advantages will appear from the description to follow. In the description, reference is made to the accompanying drawings, forming a part hereof, in which there is shown, by wayof illustration and not of limitation, a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial side view in elevation of an industrial sifter incorporating the present invention,

, FIG. 2 is a partial front view in elevation of the sifter of FIG.

FIG. 3 is a fragmentary view in cross section through the plane 3-3 shown in FIG. 4, 7

FIG. 4 is a view in cross section through the plane 4-4 shown in FIG. 1, and

FIG. 5 is a fragmentary view in cross section through the plane 5-5 shown in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT The sifter shown in the drawings includes a housing or air column enclosure, designated generally by the reference numeral 1, which is supported on vertical corner posts 2. The posts 2 are suitably interconnected, as by bottom crossmembers 3, a portion of one of which can be seen in FIG. 1, so as to form a frame; and the frame is preferably designed so that two or more units can be stacked for a sequential sifting operation.

The housing 1 includes a screen housing portion 4, which is directly supported by the posts 2, and a vibrator housing 5 which is supported on the screen housing 4. As seen most clearly in FIG. 1, the screen housing 4 has a generally U- shaped configuration and defines a rear air chamber portion 6 and a front inlet and operating portion 7. The screen housing 4 is made of metal or another suitably rigid material, and thus the reciprocating air movement therein causes little or no vibration of the walls and minimal sound transmission. Because it is rigid and fully enclosed, however, the housing 4 must be of substantial volume to allow sufficient air movement; and the U configuration of the housing 4 is advantageous in this regard in that the desired volume can be incorporated in a unit of minimum height. Other configurations are, however, possible. The actual volume and configuration for any unit will depend on various factors known to those skilled in the art, and one important consideration is that the effective length of the housing should not be such as to allow the development of standing waves.

The screen housing portion 7 includes a neck 8 of rectangular configuration which supports a screen 9 and a hopperlike inlet section 10 atop the neck 8 which supports the vibrator housing 5. As can be seen in FIG. 5, the screen 9 includes a rigid support rim 11, which rests on side and rear flanges at the top of the neck 8 and extends over the forward edge of the neck, and a screen 12 of suitable mesh which is soldered or otherwise fixed thereto. A waste or heavies" outlet passage 13 leads from the forward edge of the screen 9 and is bifurcated to terminate in dual outlet noules 14. Material not sifted through the screen 9 will pass out through the nozzles 14 and can be passed on for use or further sifting or disposed of. The bifurcated construction of the outlet passage is important in reducing the overall height of the unit, although other constructions are possible. The reason for this is that, especially for fine materials, it is necessary to have the sidewalls at angles not too far from vertical in order to insure that the material will slide down. Given a' screen of the width shown and sidewalls of the necessary angles meeting at a single nozzle, the nozzle would be substantially below the nozzles 14. The bifurcated construction effectively divides the screen 9 in half and correspondingly reduces the overall vertical dimension required for the outlet passage 13, and still provides vertical outside walls and steeply angled inner walls 13' to insure material movement.

The inlet section 10 rests on the neck 8 and includes a skirt flange 15 which surrounds the neck 8 and the top of the outlet passage 13, suitable gaskets being provided to insure an effective seal. The section 10 is connected to L-shaped arms 16, one of which is seen in FIG. I, which are in turn pivotally connected to brackets 17 fixed to the top of the housing 4. As a result, the inlet 10, and the housing 5, can be pivoted clockwise as seen in FIG. I to expose the screen 9. The screen 9 rests loosely on the neck 8 and can be removed when thus exposed, but when the section is in the normal operating position shown the screen 9 is firmly clamped between it and the neck 8. Releasable clamps 18, only one of which can be seen, are provided on both sides to hold the section 10 in place.

The section 10 is provided with an interior wall 19, the bottom portion of which is seen in H0. 5, which, with the rear wall, defines an inlet passage leading to the rear edge of the screen 9. Two inlet tubes 21, only one of which can be seen, lead into the passage 20 and can be connected to a supply of material to be sifted. A flexible metal sheet 22 extends across the bottom of the passage 20 and serves as a gate to control flow therethrough. The gate 22 is flexed to vary flow by means of a rotatable cam rod 23 suitably mounted on the sidewalls of the inlet 10 and operated by an outside knob 24.

The bottom portion of the housing 4 is also bifurcated to define two outlet nozzles 25 for fines" which have passed through the screen 9. Again, the bifurcated construction is advantageous in reducing overall height, which is particularly important where two units are to be stacked.

The outlet nozzles 14 and 25 and inlet nozzles 21 all constitute openings in the screen housing 6, but they are all quite small and have a negligible effect so far as this invention is concerned. The housing 6 can still fairly be said to be fully enclosed notwithstanding these openings.

The top of the inlet section 10 is closed off by a cover 26 which fits over the section 10 and is suitably fastened thereto with suitable gasketing between the two to provide an effective seal. The cover 26 is shaped to define a circular central opening 27, which is surrounded by an upstanding rim 28.

The vibrator housing 5 is also made of metal or another suitably rigid material and is also fully enclosed. It comprises a dome-shaped upper portion 29 and a downwardly depending circular skirt portion 30 which surrounds and is concentric with the opening 27. The housing 5 may be of any suitable configuration but should be large enough for air movement and should not allow standing waves to form. The bell jar shape shown is preferred since it provides maximum strength and thus allows the use of sheet material of uniform thickness. Other shapes might necessitate extra thickness or bracing in certain areas.

Mounted within the housing 5 is a sonic vibrator 31 which in the preferred embodiment comprises a conventional dynamic loudspeaker of suitable size and other characteristics. The mounting flange of the vibrator 3] is connected to the housing 5 by bolts 32, only one of which can be seen, which also serve to hold the housing portions 29 and 30 together, again with suitable gaskets interposed between the parts. The speaker 31 is thus mounted above and in facing alignment with the opening 27. Also held in place by the bolts 32 is a flat metal shield 33 with a large central opening 34 in alignment with the speaker cone 35. The shield 33 is of sufficient extent to blank off the edges of the speaker cone 35 and thus prevent undesirable edge effects which might interfere with proper air movement.

An elastic tuning diaphragm 36, of any suitable material such as a polyurethane, is stretched across the vibrator housing skirt 30 and is held thereon by a conventional strap fastener 37. When the housing 5 is in place, as shown most clearly in FIG. 3, the diaphragm 36 is stretched across the screen housing rim 28 so as to be interposed in and across the air column defined by the housing portions 4 and 5. The tension of the diaphragm 36, and therefore the mechanical resistance to air movement in the enclosure, can be varied by moving the housing 5 toward or away from the housing 4, which respectively stretches or relaxes the diaphragm 36. An edge portion of the diaphragm 36 lies outwardly of the rim 28 and thus is outside of the enclosure, but as in the case of the inlet and outlet nozzles, this minor portion does not appreciably affect operation and the housing 5 can be fairly said to be fully enclosed.

The housings 4 and 5 are connected by three equidistant posts 38, and these also serve as means to adjust the diaphragm 36. Each of the posts 38 is like that shown clearly in FIG. 3, except that the other two need not have the bevel gear shown, and is rotatably received through an upper boss 39 attached to the inside of the housing dome 29, a downwardly facing portion of the wall of the dome 29, and a lower boss 40 formed in or attached to the outside of the dome. The post 38 has an enlarged sprocket head 41 and an enlarged intermediate portion 42 and these enlargements engage, respectively, the bosses 39 and 40 so that while the post 38 is free to rotate it is held securely against axial movement. The lower ends of the posts 38 are threaded, and these threaded ends are received in threaded sleeves 43 fixed to the cover 26, The housing 5 is thus connected to the housing 4, and further rotation of the posts 38 will move it closer or further away to vary the tension of the diaphragm 36.

The sprocket heads 41 of the three posts 38 are mechanically linked by a chain 44 which, as can be seen in FIG. 4, extends across the housing 5 above the vibrator 31. Thus, rotation of one post 38 will result in corresponding rotation of all three. Such rotation is effected by means of an operating shaft 45 which is rotatably received through the sidewall of the dome 29 and which has an operating knob 46 at its outer end and a bevel gear 47 at its inner end which is in mesh with a bevel gear 48 formed at the top of the head 41 of the associated post 38. Rotation of the knob 46 will cause simultaneous rotation of all three posts 38.

In operation, the sifter is assembled as shown, and the material to be sifted is fed into the inlets 21 and moves onto the screen 9. Material which passes through the screen 9 goes out through the nozzles 25, and the remaining material moves across the screen 9, which is preferably slightly tilted down from front to rear to aid such movement, and out through the nozzles 14. The speaker 31 is operated during sifting, preferably off a standard 60 cycle AC supply (not shown) and establishes a reciprocating air movement which greatly enhances the sifting action, all as previously known.

Because the air column defined by the housings 4 and 5 is fully enclosed and rigid, the reciprocating air movement will not cause the vibrations and noise common to sifters with exposed diaphragms, and the sifter of this invention is dramatically quieter than known industrial sifters of this type.

The diaphragm 36 allows for tuning of the sifter and, therefore, maximum efficiency. The mechanical resonant frequency, or natural frequency, of speakers or other vibrators used for sifters of this type is usually less than 60 cycles per second, and while the enclosure and material being sifted adds resistance the net natural frequency would still be less than 60 cycles without the diaphragm 36. The extra resistance which can be added by the diaphragm 36 is enough, however, to bring the mechanical frequency to approximately 60 cycles so as to have maximum efficiency.

Having the diaphragm 36 effectively entirely within the air column allows for tuning without the noise problem caused by externally exposed diaphragms. The mechanical tuning system comprising the posts 38 and associated elements allows for easy and effective tuning, while the sifter is running, even though the diaphragm is within the air column. Having the diaphragm 36 between the speaker and screen housings and attached directly to the speaker housing is particularly advantageous in that when the speaker housing 5 is removed for any reason, the diaphragm 36 stays with it and serves as a dust and general protective cover for the speaker cone 35, which would otherwise be exposed.

Although a preferred embodiment of the invention has been shown and described, it will be obvious that modifications might be made without departure from the invention. Ancillary features like or similar to the tapper and photoelectric control shown in the aforementioned Ward patent might be added. Other forms of vibrators might be used. The sifter need not be used only with a 60 cycle supply, and the same principle could be used for tuning to any reasonable frequency. The diaphragm need not necessarily be between the speaker and screen and could be elsewhere in the air column. Other mechanical tuning systems might be used. and changes could be made in the housing configuration or other parts. In view of the many possible modifications, the invention is not intended to be limited by the showing herein, or in any other manner, except as may specifically be required by the following claims.

I claim:

1. In a reciprocating air column sifter having a screen housing and a speaker housing connected thereto and in communication therewith through an opening, there being a screen in the screen housing and a speaker means in the speaker hous' ing which faces the screen for establishing a reciprocating air movement therethrough,

the improvement wherein:

the screen and speaker housings are substantially imperforate and together define a rigid. fully enclosed air column; and there is an elastic tuning diaphragm across the air column which faces the speaker; and there is means to adjust the tension of the diaphragm to vary the natural mechanical resonant frequency of the sifter.

2. A sifter according to claim 1 wherein the screen and speaker housings have facing openings; and the diaphragm is mounted on and seals off the opening of one of the housings; and the opening of the other housing is surrounded by an upstanding rim across which the diaphragm is stretched; and the housings are connected by means of threaded posts which can be tightened or loosened to vary the tension of the diaphragm.

3. A sifter according to claim 2 wherein there are at least three threaded posts spaced about the openings; and each post has a sprocket; and there is a chain extending about and linking the several posts; and there is an operating means to rotate one post, the chain then serving to cause simultaneous corresponding movement of the other posts.

4. The sifter of claim 3 wherein the speaker housing is fully removable from the screen housing; and the diaphragm is mounted on and seals off the opening in the speaker housing. 

1. In a reciprocating air column sifter having a screen housing and a speaker housing connected thereto and in communication therewith through an opening, there being a screen in the screen housing and a speaker means in the speaker housing which faces the screen for establishing a reciprocating air movement therethrough, the improvement wherein: the screen and speaker housings are substantially imperforate and together define a rigid, fully enclosed air column; and there is an elastic tuning diaphragm across the air column which faces the speaker; and there is means to adjust the tension of the diaphragm to vary the natural mechanical resonant frequency of the sifter.
 2. A sifter according to claim 1 wherein the screen and speaker housings have facing openings; and the diaphragm is mounted on and seals off the opening of one of the housings; and the opening of the other housing is surrounded by an upstanding rim across which the diaphragm is stretched; and the housings are connected by means of threaded posts which can be tightened or loosened to vary the tension of the diaphragm.
 3. A sifter according to claim 2 wherein there are at least three threaded posts spaced about the openings; and each post has a sprocket; and there is a chain extending about and linking the several posts; and there is an operating means to rotate one post, the chain then serving to cause simultaneous corresponding movement of the other posts.
 4. The sifter of claim 3 wherein the speaker housing is fully removable from the screen housing; and the diaphragm is mounted on and seals off the opening in the speaker housing. 